The "Windows 8/2012 sideloading crack", offered via a post on My Digital Life Forums, enables the installation of not-yet approved Windows Store apps as well as the conversion of trial versions to full versions.
According to the FAQ, the software can also create redistributables of already purchased applications - and especially those that are offered as a buy option only: "Someone [has] to buy it, prepare redistributable and share with others. It's like ripping blueray. Someone has to buy the disc."
The crack was apparently released shortly after the release of Windows 8, and has been modified several times since then. However, there are still shortcomings, such as the fact that cracked apps cannot be updated via the Windows Store.
Microsoft has not yet reacted to the crack, but the issue appears to be significant enough to be addressed sooner rather than later.